1. (Technical Field of the Invention)
The present invention relates to a starter for starting an engine and, more particularly, the present invention relates to a starter having a structure that reduces operation noise thereof.
2. (Related Art)
Conventionally, automatic engine stop/restart systems (hereinafter referred to as “idle stop system(s)”) are known. Such an idle stop system is able to automatically control stop/restart of an engine.
Specifically, Japanese patent Laid-open Publication No. 2005-330813 discloses an idle stop system. The idle stop system includes a pinion control means for controlling the pinion gear to be pushed out towards a ring gear and a motor control means for controlling current to be supplied to the motor on/off. In the idle stop system, the pinion control means and the motor control means are configured such that the both means can be operated individually. With this configuration, even if an event requiring an engine-restart occurs during the engine rotation is decreasing until the engine completely stopped, the pinion gear is pushed out to the ring gear while being rotated whereby the pinion gear meshes with the ring gear. As a result, the engine-restart can be made by powering the motor after completion of the meshing, With this method applied to this configuration, compared to the engine-restart being made after the complete engine stop, the driver of the vehicle does not feel anything uncomfortable because of the smooth engine-restart.
According to the above-described prior art, even if the engine-restart request is not issued while the engine rotation is decreasing, the pinion gear can be meshed with the ring gear when the rotation speed of the ring gear reaches a predetermined value. Subsequently, the meshing between pinion gear and the ring gear can be maintained until the complete engine stop without powering the motor. Therefore, since the pinion gear and the ring gear remain meshed when next engine-restart request occurs, necessary period for the engine-restart can be reduced.
An increase in vehicles including an idle-stop system that automatically controls stop and restart of the engine is expected in the next few years. As the vehicles including the idle stop system increase, for instance, it is expected situations that vehicles become stuck in a local road due to a traffic jam. In this case, it is considered that the engines in the vehicles start at almost the same time. As a result, operation noise of the starter when the engine starts increases and such a noise may cause a noise pollution problem along the road side.
The dominant noise elements accounting for the operation noise of the starter includes a strike noise that occurs when the end face of the pinion gear strikes the end face of the ring gear, a strike noise caused by the teeth faces of the pinion gear and the ring gear when the pinion gear meshes with the ring gear, and an operation noise of the electromagnetic solenoid which is a part of the pinion control means (i.e., a strike noise that occurs when a plunger strikes a core).
However, as described above, when the pinion gear meshes with the ring gear while the engine rotation is decreasing without supplying power to the motor, the end face of the pinion gear strikes the end face of the ring gear and at almost the same time, the plunger of the electromagnetic solenoid strikes the core. As a result, two types of noises caused by both striking influence each other and generate an impact noise that accumulates the noises. Moreover, at the moment, since the motor is not powered so that no operation sound is generated by the motor. Hence, the above-described impact noise significantly stands out and makes the driver of the vehicle uncomfortable.